“Promoting another course, eBook, or program in which they must buy, there’s a good chance you’re going to get turned off eventually. A good rule of thumb is to give your reader 10x more. Instead, offer freebies just so they will warm up to you.”
When readers notice your email in their inbox, they should see a source of valuable information for them. Not blaring links to purchase products or sign up for courses. They’ll get turned off.